Stress and/or Field Induced Magnetic Anisotropy in the Amorphous Fe73.5Cu1Nb3Si15.5B7 Alloy: Influence on the Coercivity, Saturation Magnetostriction and Magneto-Impedance Response

Abstract

The effect of different kinds of annealing on the magnetic behavior in Fe 73.5 Cu 1 Nb 3 Si 15.5 B 7 amorphous alloy has been investigated. Three different kinds of the current annealing (current densities ranging from 30 to 49 A/mm 2 with a duration up to 120 s) were carried out: 1. under tensile stress (500 MPa); 2. under axial magnetic field (750 A/m); 3. under tensile stress (500 MPa) + magnetic field (750 A/m). As a result of these thermal treatments, a uniaxial in-plane magnetic anisotropy can be induced in the annealed samples. The easy axis of this induced anisotropy at low current densities ( 45 A/mm 2 ) the easy axis results to be parallel to the direction of the ribbon for the three kinds of treatment. Dependence of the induced anisotropy with the current density shows a maximum (250 J/m 3 ) around 45 A/mm 2 , related to the optimum structural relaxation of the amorphous state. A decrease of the induced anisotropy, observed at 45-49 A/mm 2 , should be ascribed to the first stages of the nanocrystallization process. Similar behavior was obtained for the coercivity of the samples after these thermal treatments. A very low value of the coercivity (about 1 A/m) has been achieved after magnetic field annealing. Variations of the saturation magnetostriction with the current density are reported for the samples treated by stress and stress + field annealing. Results on the magneto-impedance effect in these stress and/or field annealed sample (changes around 10-15%) are also presented.